Role of the Insula and Vestibular System in Patients with Chronic Subjective Dizziness: An fMRI Study Using Sound-Evoked Vestibular Stimulation.

Chronic subjective dizziness (CSD) is a common vestibular disorder characterized by persistent non-vertiginous dizziness, unsteadiness, and heightened sensitivity to motion stimuli that may last for months to years after events that cause acute vestibular symptoms or disrupt balance. CSD is not associated with abnormalities of basic vestibular or oculomotor reflexes. Rather, it is thought to arise from persistent use of high-threat postural control strategies and greater reliance on visual cues for spatial orientation (i.e., visual dependence), long after triggering events resolve. Anxiety-related personality traits confer vulnerability to CSD. Anomalous interactions between the central vestibular system and neural structures related to anxiety may sustain it. Vestibular- and anxiety-related processes overlap in the brain, particularly in the insula and hippocampus. Alterations in activity and connectivity in these brain regions in response to vestibular stimuli may be the neural basis of CSD. We examined this hypothesis by comparing brain activity from 18 patients with CSD and 18 healthy controls measured by functional magnetic resonance imaging during loud short tone bursts, which are auditory stimuli that evoke robust vestibular responses. Relative to controls, patients with CSD showed reduced activations to sound-evoked vestibular stimulation in the parieto-insular vestibular cortex (PIVC) including the posterior insula, and in the anterior insula, inferior frontal gyrus, hippocampus, and anterior cingulate cortex. Patients with CSD also showed altered connectivity between the anterior insula and PIVC, anterior insula and middle occipital cortex, hippocampus and PIVC, and anterior cingulate cortex and PIVC. We conclude that reduced activation in PIVC, hippocampus, anterior insula, inferior frontal gyrus, and anterior cingulate cortex, as well as connectivity changes among these regions, may be linked to long-term vestibular symptoms in patients with CSD. Furthermore, altered connectivity between the anterior insula and middle occipital cortex may underlie the greater reliance on visual cues for spatial orientation in CSD patients relative to controls.

Accuracy of magnetic resonance parkinsonism index for differentiation of progressive supranuclear palsy from probable or possible Parkinson disease.

BACKGROUND: Combined measurements on conventional magnetic resonance imaging (MRI), such as midbrain area/pons area or magnetic resonance parkinsonism index (MRPI) (pons area/midbrain area × middle cerebellar peduncle width/superior cerebellar peduncle width), have been proposed as powerful tools in the differential diagnosis between progressive supranuclear palsy (PSP) and Parkinson disease (PD). In this study, we evaluated the accuracy of MRPI, compared with midbrain/pons ratio, in distinguishing PSP from probable and possible PD. METHODS: Forty-two PSP patients, 170 probable PD patients, 132 possible PD patients, and 38 control subjects underwent MRI and, for each patient, midbrain/pons ratio and MRPI were calculated. RESULTS: Midbrain/pons ratio showed low accuracy in distinguishing PSP patients from those with probable PD (92.9% sensitivity; 85.3% specificity; 86.8% diagnostic accuracy) or those with possible PD (88.1% sensitivity, 88.3% specificity, and 88.2% diagnostic accuracy) and control subjects (97.6% sensitivity, 92.1% specificity, and 95% diagnostic accuracy). By contrast, MRPI showed higher accuracy to distinguish PSP from probable PD (100% sensitivity, 99.4% specificity, and 99.5% diagnostic accuracy), from possible PD (100% sensitivity, 99.2% specificity, and 99.4% diagnostic accuracy), and from control subjects (sensitivity, specificity, and diagnostic accuracy of 100%). CONCLUSIONS: Our study confirms that MRPI is a more accurate measure than midbrain/pons ratio for differentiation of patients with PSP from those with probable and possible PD.

An magnetic resonance imaging T2*-weighted sequence at short echo time to detect putaminal hypointensity in Parkinsonisms.

At 1.5 T, T2*-weighted gradient echo (GE) sequences are more sensitive in revealing mineral deposition in the basal ganglia than standard T2 weighted sequences. T2*-weighted GE sequences, however, may detect putaminal hypointensities either in patients affected by parkinsonian syndromes or in healthy subjects. The aim of this study was to identify the magnetic resonance imaging (MRI) T2*-weighted sequence which more specifically detected putaminal hypointensities differentiating atypical parkinsonian syndromes from Parkinson's disease (PD) and control subjects. In a sample of 38 healthy subjects, we performed three T2*-weighted GE sequences at increasing time echo (TE; TE = 15 millisecond, TE = 25 millisecond, and echoplanar at TE = 40 millisecond; T2* sequences study). The sequence not showing any putaminal abnormality in the healthy subjects was then used to assess putaminal signal intensity in 189 patients with PD, 20 patients with multiple system atrophy (MSA), 41 patients with progressive supranuclear palsy (PSP), and in 150 age and sex-matched control subjects. In the T2* sequences study, the T2*-weighted TE = 15 (T2*/15) did not show any putaminal abnormalities in the healthy subjects. This sequence detected putaminal hypointensities in a significantly higher proportion of patients with MSA (35%, P < 0.05) and PSP (24.4%, P < 0.05) than in patients with PD (5.3%), but in none of the controls. The sensitivity of putaminal hypointensity in T2*/15 sequence was 25.4% for PD, 43.9% for PSP, and 55% for MSA versus controls whereas the specificity was 93.2% for all groups. Despite the suboptimal sensitivity, the high specificity of the T2*/15 sequence performed on routine MRI suggests its usefulness in clinical practice for identifying putaminal hypointensities associated with parkinsonian disorders.

Fronto-parietal overactivation in patients with essential tremor during Stroop task.

Neuropsychological dysfunctions have been consistently reported in essential tremor but the underlying neurobiological mechanisms are unknown. We explored potential abnormalities in the neural network involved in cognitive functions in patients with essential tremor by using functional magnetic resonance imaging. The functional response of 12 patients with essential tremor and 12 matched controls was studied while performing a functional magnetic resonance imaging Stroop task aimed to assess attentional control and evaluating executive functions. Despite similar performances during this task, patients with essential tremor showed greater magnitude of brain response in the dorsolateral prefrontal cortex and in the inferior parietal cortex with respect to controls. Our study shows that patients with essential tremor require additional cognitive effort to achieve comparable performance levels on test of attentional control.

Combined use of DAT-SPECT and cardiac MIBG scintigraphy in mixed tremors.

The cooccurrence of rest and postural tremor (mixed tremor) as the predominant clinical manifestation in patients who do not fulfill diagnostic established criteria for essential tremor (ET) or Parkinson's disease (PD) poses a clinical diagnostic challenge. Twenty-two patients with mixed tremor and additional mild extrapyramidal features, such as bradykinesia and rigidity, 20 patients with probable PD, 10 patients with probable ET, and 18 controls were investigated through the combined use of dopamine transporter (123)I-FP-CIT-single-photon emission tomography (DAT-SPECT) and cardiac (123)metaiodobenzylguanidine (MIGB) scintigraphy. Six of the 22 mixed-tremor patients had normal DAT-SPECT, a condition usually found in patients with ET, whereas 16 patients showed damage to the nigrostriatal system. Cardiac MIBG allowed further differentiation between these 16 patients because eight of them had decreased tracer uptakes (heart/mediastinum [H/M] ratio in delayed image, H/M ratio delayed: 1.16 +/- 0.11, P < 0.001 vs controls), indicating a PD, whereas the remaining eight had normal cardiac tracer uptakes, a finding suggestive of a parkinsonian syndrome (H/M ratio delayed: 1.90 +/- 0.13). Both DAT-SPECT and cardiac MIBG scintigraphies were abnormal in the 20 patients with probable PD, whereas these were normal in both the patients with probable ET as well as in the controls. Our study suggests that the combined use of both DAT-SPECT and MIBG scintigraphy in mixed tremors with additional extrapyramidal features can help distinguish patients with ET from those with PD and parkinsonism.